Large logo images break Firefox login box layout
Large logo images break Firefox login box layout

Fixes: CNVS-23773

Bug: http://cl.ly/image/02280f0m3f1f
Fixed: http://cl.ly/image/2W3v0j2m3v2p

Test plan:
- Turn on the new UI and open Theme Editor in
  FIREFOX
- Customize the login screen with a custom logo
  image file. Make sure it's wider than 190px.
- Save your changes in Theme Editor and log out
  of Canvas
- The login screen should now show your new logo
  image at the top of the box (you may or may not
  see the other header links, based on your account
  settings).
- The logo should not exceed 190px in width now.

Change-Id: I2613ce9a1470b65c5ca944a252783f362302e836
Reviewed-on: https://gerrit.instructure.com/64430
Tested-by: Jenkins
Reviewed-by: Colleen Palmer <387ba1943871e60965e6b44638a2f2e1ab9b8469@instructure.com>
Product-Review: Colleen Palmer <387ba1943871e60965e6b44638a2f2e1ab9b8469@instructure.com>
QA-Review: Nathan Rogowski <2e8aa918660411855c6d44d5bb2da677aa033255@instructure.com>

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